A quantity is a property of a concept.
For example, height is a property of our concept of a person. The property, height, is a distance or span from the soles of a person's feet to the top of her or his head. Note that "people in our class" and "family" are NOT quantities. We have a concept of people in our class, but to make a quantity we have to identify a property of that concept. Similarly, we have a concept of our family, but to make a quantity we have to identify a property of that concept. What are some properties we could identify to make "family" into a quantity?
Finding a numerical value of a quantity involves identifying a unit, imagining the property subdivided into some number of those units, and then actually doing the subdividing and counting up the number of units in some way!
For example, to find a value for the height of a person one could consider the height divided up into segments the size of a standard toothpick. Then we would have to count up the number of those segments.
Does a quantity only have one value?
How is counting involved in using feet or inches to measure the height of a person?
What is not a quantity?
It's hard to quantify emotions like love, sadness, happiness; memories; and ideals like peace, freedom, and integrity. These are usually referred to as qualities, or as qualitative. It's also hard to quantify sensory perceptions like sound and smell and touch, although there are ways to do it (consider in hospitals when doctors ask you to rate the pain you're feeling on a scale of 1 to 10)!
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An unknown quantity is the potential measurement of a quantity. This means a value of the quantity is as of yet unknown but has the potential to be known through counting (or some other means, e.g., calculation). Note that we can reason with quantities even when they are unknown!
A known quantity is a quantity for which a value is known.
The size of the unit will affect the numerical value of a quantity. Can you explain how?
On Quantity
A quantity is a property of a concept.
For example, height is a property of our concept of a person. The property, height, is a distance or span from the soles of a person's feet to the top of her or his head.
Note that "people in our class" and "family" are NOT quantities. We have a concept of people in our class, but to make a quantity we have to identify a property of that concept. Similarly, we have a concept of our family, but to make a quantity we have to identify a property of that concept. What are some properties we could identify to make "family" into a quantity?
Finding a numerical value of a quantity involves identifying a unit, imagining the property subdivided into some number of those units, and then actually doing the subdividing and counting up the number of units in some way!
For example, to find a value for the height of a person one could consider the height divided up into segments the size of a standard toothpick. Then we would have to count up the number of those segments.
What is not a quantity?
It's hard to quantify emotions like love, sadness, happiness; memories; and ideals like peace, freedom, and integrity. These are usually referred to as qualities, or as qualitative. It's also hard to quantify sensory perceptions like sound and smell and touch, although there are ways to do it (consider in hospitals when doctors ask you to rate the pain you're feeling on a scale of 1 to 10)!
More on quantity...